The disclosure of Japanese Patent Application No. 2000-294739 filed on Sep. 27, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a vehicle braking and driving force control apparatus and a control method thereof. It relates more particularly to a vehicle braking and driving force control apparatus having a frictional braking device for applying a braking force individually to each wheel, and a regenerative braking device for applying a common braking force to a plurality of wheels, and to a control method thereof.
2. Description of Related Art
A well-known vehicle braking force control apparatus of an automobile and the like comprises, for example as disclosed by the present applicant in Japanese Patent Application Laid-Open No. 11-105688, a regenerative braking device and a frictional braking device (hydraulic braking device), in which both regenerative braking force and frictional braking force are increased when there is a need to suddenly increase the braking torque at the time of traction control, and in which the frictional braking force is kept constant and the regenerative braking force is decreased gradually when there is a need to gradually decrease the braking torque.
According to such braking force control apparatus, the braking torque can be increased quickly or decreased smoothly by making use of the characteristics of the regenerative braking device and the frictional braking device. Thus, the traction is controlled by using both regenerative braking force and frictional braking force, and therefore as compared with the case of use of the frictional braking force only at the time of traction control, the regeneration efficiency is enhanced and the fuel consumption of the vehicle is improved.
In the conventional braking force control apparatus as described above, however, since the regenerative braking device and the frictional braking device are not controlled so as to enhance the regeneration efficiency when applying a braking force to the wheels at the time of traction control, from the viewpoint of the regeneration efficiency, the regenerative braking device and the frictional braking device are not used most efficiently, and hence there is room for improvement in this respect in the conventional braking force control apparatus.
The invention is devised in light of the above problems of the conventional braking force control apparatus for vehicles comprising a regenerative braking device and a frictional braking device. It is a primary object of the invention to enhance the regeneration efficiency in a situation of automatic and individual control of a braking force or a driving force of each wheel during motion control of a vehicle, by using the regenerative braking device and the frictional braking device so as to achieve a high regeneration efficiency in a situation of automatic and individual control of the braking force or the driving force of each wheel by motion control of the vehicle such as traction control.
This and/or other objects are achieved by a braking and driving force control apparatus for a vehicle having a frictional braking device for applying a braking force individually to each wheel, and a regenerative braking device for generating a common braking force to a plurality of wheels. According to one aspect of the invention, the braking and driving force control apparatus includes a controller that: (a) calculates a target braking force of each wheel in response to a running state of the vehicle; and (b) controls the frictional braking device and the regenerative braking device so that the braking force of each wheel becomes the target braking force, in which the controller controls the regenerative braking device so as to achieve the smallest target braking force of the target braking forces of the plurality of wheels, and controls the frictional braking device so as to achieve the target braking force of another wheel, different from the wheel having the smallest target braking force, in cooperation with the regenerative braking device.
The object is also achieved by a braking and driving force control method for a vehicle having a frictional braking device for applying a braking force individually to each wheel, and a regenerative braking device for generating a common braking force to a plurality of wheels, comprising the steps of:
calculating a target braking force of each wheel in response to a running state of the vehicle;
controlling the regenerative braking device so as to achieve the smallest target braking force of the target braking forces of the plurality of wheels; and
controlling the frictional braking device so as to achieve the target braking force of another wheel, different from the wheel having the smallest target braking force, in cooperation with the regenerative braking device.
According to such braking and driving force control apparatus and method, as for the wheel with the smallest target braking force, the target braking force is achieved by the regenerative braking force, and as for the other wheels, the target braking force is achieved by the sum of the regenerative braking force and the frictional braking force. Therefore, each wheel can be braked at the highest regeneration efficiency in a situation of automatic control of the braking force or the driving force of each wheel during motion control.
Another aspect of the invention relates to a braking and driving force control apparatus for a vehicle having a frictional braking device for applying a braking force individually to each wheel, a regenerative braking device for generating a common braking force to a plurality of wheels, and a drive device for generating a common driving force to the plurality of wheels. The braking and driving force control apparatus includes a controller that: (a) calculates a target braking force of each wheel in response to a running state of the vehicle; (b) calculates a target driving force of each wheel in response to the running state of the vehicle; and (c) controls the frictional braking device, the regenerative braking device, and the drive device so that the braking and driving force of each wheel becomes the target braking and driving force on the basis of the target braking force and target driving force. The controller calculates the entire target driving force of the plurality of wheels on the basis of the target driving force of each wheel, and calculates the entire target braking and driving force of the plurality of wheels on the basis of the entire target driving force of the plurality of wheels and the smallest target braking force of the target braking forces of the plurality of wheels. When the entire target braking and driving force of the plurality of wheels is a driving force, the controller controls the drive device so as to achieve the entire target braking and driving force of the plurality of wheels, and controls the frictional braking device so as to achieve the target braking force of another wheel, different from a wheel having the smallest target braking force. When the entire target braking and driving force of the plurality of wheels is a braking force, the controller controls the regenerative braking device so as to achieve the entire target braking and driving force of the plurality of wheels, and controls the frictional braking device so as to achieve the target braking force of the another wheel, different from the wheel having the smallest target braking force in cooperation with the regenerative braking device.
The object is also achieved by a braking and driving force control method for a vehicle having a frictional braking device for applying a braking force individually to each wheel, a regenerative braking device for generating a common braking force to a plurality of wheels, and a drive device for generating a driving force to the plurality of wheels, comprising the steps of:
calculating a target braking force and a target driving force of each wheel in response to a running state of the vehicle;
calculating the entire target braking and driving force of the plurality of wheels on the basis of the entire target driving force of the plurality of wheels and the smallest target braking force of the target braking forces of the plurality of wheels;
when the entire target braking and driving force of the plurality of wheels is a driving force, controlling the drive device so as to achieve the entire target braking and driving force of the plurality of wheels, and controlling the frictional braking device so as to achieve the target braking force of another wheel, different from a wheel having the smallest target braking force, and
when the entire target braking and driving force of the plurality of wheels is a braking force, controlling the regenerative braking device so as to achieve the entire target braking and driving force of the plurality of wheels, and controlling the frictional braking device so as to achieve the target braking force of the another wheel, different from the wheel having the smallest target braking force, in cooperation with the regenerative braking device.
According to such braking and driving force control apparatus and method, when the entire target braking and driving force of the plurality of wheels is a driving force, since the frictional braking device and drive device are controlled so as to achieve the target braking force and target driving force of each wheel, control of the braking force and driving force of each wheel by motion control can be achieved reliably. Similarly, when the entire target braking and driving force of the plurality of wheels is a braking force, since the frictional braking device and regenerative braking device are controlled so as to achieve the target braking force and target driving force of each wheel, the target braking force is achieved by the regenerative braking force as for the wheel having the smallest target braking force, while the target braking force is achieved by the sum of the regenerative braking force and the frictional braking force as for the other wheels. Therefore, each wheel can be braked at the highest regeneration efficiency in a situation of automatic and individual control of braking force or driving force of each wheel by motion control.